Light emitting devices which radiate light perpendicular to the substrate can be easily coupled to optical fibers and are expected to find various uses as surface emitting light sources. Efforts have therefore been made to develop these devices in the field of research on laser diodes and light emitting diodes, and a wide variety of such devices are in use in recent years.
With the conventional perpendicular radiationtype or surface emitting-type light source device, however, the pn junction is positioned in parallel with the substrate to provide an active region which is usually as small as 2 to 3 .mu.m in thickness. Consequently, a gain which is needed for causing the device of this type to produce laser oscillation of sufficient intensity perpendicular to the substrate. Thus, the device substantially has the fatal drawback that it is difficult to realize continuous oscillation at room temperature as essentially required of useful laser diodes.
Generally speaking, in the field of various systems such as those of optical communication and optical information transference or various optical industrial techniques for manufacturing optical diodes, optical memories and the like, the research and the development of various kinds of semiconductor laser devices, photodiodes and the like as for the source for generating the light regarded as the subject thereof are actively performed. However, in the most of highly efficient semiconductor laser devices which have been conventionally developed, the confinement of carriers and lights is effectively carried out by employing a wafer having double hetetostructure, so that the resultant lights are emitted in the direction parallel with the substrate of the device, as well as the injection of the carriers is effected in the direction of thickness thereof.
On the other hand, the so-called "facial light emitting" device constructed such as the resultant light is emitted in the direction of thickness perpendicular to the device substrate is widely used in the from of light emitting diode. The light emitting device of this kind has been developed as regarded as a light emitting diode having a wide light emitting surface, meanwhile the possibility of realization of a facial light emitting device provided with the function of semiconductor laser.
The conventional facial light emitting device of this kind, particularly, the conventional facial light emitting semiconductor laser device is constructed as shown in FIG. 1, that is, as operated as a laser device by basically forming an optical resonator in a manner such as clad layers and a reflector layer are provided on an upper and a lower surfaces of an active region of a facial light emitting type light emitting diode, the latter being sandwiched by the formers.
Concretely speaking, in the crosssectional view of the structure as shown in FIG. 1, an intermediate layer 1 having thickness d is sandwiched by clad layers 2 and 3 consisting of a material having a wide energy gap, so as to form a sandwich structure. Among the clad layers 2 and 3 in this exemplified structure, the thicker clad layer 2 as shown in FIG. 1 is formed as of n-type, meanwhile the other clad layer 3 is formed as of p-type. On an upper surface and a lower surface of this sandwich structure, an annular electrode 8 and a circular electrode 6 are provided, respectively, as shown in FIG. 1, so as to form an active region 4 in the central portion of the intermediate layer 1 usually consisting of an intrinsic material and excited by making a current CF flow therethrough in a bell-bottom shape, this active region 4 only being injected with the carriers from the upper and the lower sides. In addition, the circular electrode 6 provided on the lower surface of the sandwich structure is operated as a reflective mirror, as well as a translucent mirror 7 is provided in a central blank of the annular electrode 8 provided on the upper surface of the sandwich structure, so as to form the optical resonator PR. As a result, the laser oscillation is effected, the output laser light PO resulted therefrom being taken out through the translucent mirror 7.
Accordingly, in the conventional facial light emitting device of this kind, for instance, in the conventional facial light emitting semiconductor laser device, the pn junction, through which the carriers are injected, is formed in the vertical direction, that is, in the direction of thickness of the sandwich structure and hence the thickness of the active region is restricted by the diffusion length of the carriers. As a result, for obtaining a gain for generating the laser oscillation with a sufficient intensity in the conventional facial light emitting semiconductor laser device, an extremely large injection current density is necessitated. So that, the conventional facial light emitting semiconductor laser device essentially has such a fatal defect over the merit of facial light emission that it is difficult to realize the continuous oscilation at room temperature as an unavoidable condition of the semiconductor laser device for practical use.